This invention relates generally to a method and apparatus for recording and/or reproducing digital data. More particularly, the present invention relates to a rotary head type digital audio tape recorder (R-DAT) when used for recording data from a computer or the like.
2. Description of the Prior Art
In order to protect computer generated data written on a hard disc or the like, the data are sometimes transferred to a so-called data streamer (or data recorder) and are thereby recorded (or backed up) on other recording media once per day.
In most cases, a conventional data streamer is what might be called an analog audio tape recorder. Such an analog audio tape recorder, however, consumes a great quantity of the recording medium (i.e. tape). Also, such a conventional data streamer has a low data rate upon recording so that it takes a lot of time for transferring and recording the data. Further, it is not easy for the analog audio tape recorder to find out the starting point of the desired recorded data.
When data, for example, from a computer is recorded by the use of a conventional audio tape recorder, an arbitrary file mark signal is supplied thereto from the computer. Upon reproduction, the location number of the file mark for the computer designated address is searched for. Since the conventional analog audio tape recorder is so arranged as to search for the location number of the file mark by counting the reproduced signal of the file mark in the normal reproduction operation, it takes a long time to search for the desired file mark. Thus, it is difficult to search for the location number of the file mark.
A DAT (digital audio tape recorder) has been developed, as described in "ES Review", pp. 11 to 14, published on December, 1985 by Sony Corporation, Shibaura Plant: ISSN 0389-7737. Since this DAT is designated so as to record and/or reproduce a digital signal that is a digitized audio signal, it is very suitable for recording the aforesaid data.
The assignee of the present application has proposed a data recorder using an R-DAT for computer in U.S. Patent Applications Ser. No. 133,010 filed Dec. 15, 1987 and Ser. No. 177,624 filed Apr. 5, 1988.
With a DAT as described above, when another signal is to be recorded on a previously recorded recording medium, previously recorded signals are erased by recording new signals over them, that is, by a so-called overwriting, without using an erasing head. Therefore, if overwriting is not normally effected, for example, due to clogging of the head, there is the possibility that a part of the previously recorded signals remains unerased.
To correct this problem, in the DAT format an error detecting code is added to each recording track so as to detect an unerased portion, if any, in the track as an error. However, even with such a code added to each track, if an entire track remains unerased no error is detected since the error detecting code within the unerased track is considered normal.
If the signal to be recorded is an audio signal, wherein adjacent data are correlated with each other due to the more or less continuous nature of an audio signal, a correction can be effected by an interpolation technique even though the remaining unerased signal portion is removed from the track. However, if the DAT is employed as a data recorder, wherein adjacent data are not generally correlated, the interpolation technique cannot be utilized.
The aforementioned U.S. Patent Application Ser. No. 177,624 filed Apr. 5, 1988 proposes a technique wherein, when the DAT is employed as a data recorder, an error correcting code is generated for a plurality of frames of data signals to be supplied to the DAT and the error correcting code thus generated is supplied to the DAT to be recorded on the tape, in the same manner as the data signals. Thus, error correction is effected outside the DAT, thereby providing the DAT with a powerful error correcting performance.
This error correcting operation requires that an erroneous frame has been detected prior to the error correcting operation. However, in the above-mentioned case where one or more tracks remain entirely unerased, the error cannot be detected by this method. Therefore, although the error correcting code is generated outside the DAT, errors cannot be corrected.